Rail pads are used in rail systems to support rails and reduce shock and vibration in a rail system which may be due, for example, to the use of the rail system for supporting a rail for a large structure such as a gantry crane.
Rail systems for supporting such structures are usually supported along their length by a resilient pad interposed between the base of the rail and a support surface for the rail such as a steel girder. The support typically lies on a concrete foundation and provides for load distribution over the foundation. The resilient pads absorb and distribute the loads that act on the rail when a wheel of the crane passes by.
Existing pads typically comprise a steel insert disposed between two rubber layers and have longitudinal grooves in their upper surface. The purpose of these grooves is to give the pad an initial softness when a vertical load, which may be due to a crane wheel running over the rail immediately above the rail pad, is applied. When the load increases the grooves flatten as the pad deforms, which causes the pad to become stiffer thereby reducing bending stresses in the rail.
The sustained loading on the rail pad can cause multiple problems in the rail pad. Lateral tearing can manifest along the edge of the steel insert, particularly where the steel insert terminates in line with the bottom of a groove so there is a very small cross section of rubber. Sustained loading on the pad also results in axial splitting along the centre of the pad and the steel insert.
The pad may also displace due to lubrication from fluids that are within the recess of a crane rail. This fluid can sit in the grooves of the pad and when a wheel from a crane passes over the rail this fluid is pushed back and forth along the longitudinal groove and cannot escape. This generates a hydraulic effect within the grooves. The presence of the fluid within the grooves means the grooves cannot flatten when a vertical load is applied which causes increased stresses on the rail pad and ultimate failure along the grooves. Such fluids may also contain water that will cause aquaplaning and subsequent lateral displacement of the rail pad.
Aspects and embodiments were devised with the foregoing in mind.